1. Field
The disclosure relates to high resolution RADAR, LIDAR and other applications. More particularly, the disclosure relates to a non-linear FM pulse compression system and method which enhances target resolution in RADAR, LIDAR and other applications.
2. Description
The word RADAR is an acronym derived from the phrase RAdio Detection And Ranging and applies to electronic equipment designed for detecting and tracking objects (targets) at considerable distances. The basic principle behind radar is simple—extremely short bursts of radio energy (traveling at the speed of light) are transmitted, reflected off a target and then returned as an echo. The RADAR system correlates the return signal (appropriately corrected for gain) with the transmitted pulse to indicate the location of the target within a two or three dimensional framework. Among the various radar processing techniques, pulse compression is a signal processing technique mainly used not only in radar but also in sonar and echography to enhance the range resolution as well as the signal-to-noise ratio.
The rectangular pulse of an electromagnetic signal is given by [1]Pr(t)=A exp(j2πfct) T/2≦t<T  (1)where fc is the carrier frequency.
The linear FM chirp of an RF signal is given byPFM(t)=A exp(−j2πfct2) T/2≦t<T  (2)
Various techniques for pulse compression of electromagnetic signals using variants of frequency modulation are known in the art. These include an AM-FM laser for improved accuracy of target range measurements and a LASER RADAR system which uses an optically linear modulated FM chirp signal (also known as a compressed high intensity radar pulse). Another method proposes a random FM scheme for mobile radios including a non-linear FM modulation which is carried out by driving an FM modulator with random or chaotic sequences and deriving theoretical expressions for the spectral properties of the FM waveforms.
The conventional FM chirp techniques mentioned above either use linear FM modulation or propose the use of random input sequences to create non-linear FM signals with the perfect auto correlation function properties. However, these techniques are either too complicated to implement in many applications or do not result in optimal pulse compression. Moreover, conventional pulse compression techniques may not result in a range resolution which is optimal for the application. Therefore, a non-linear FM pulse compression system and method which can result in an order of magnitude improvement in pulse compression and hence dramatically improve the resolution as well as the precision of range of detected targets in RADAR, LADAR and other applications is needed.